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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.api;

import java.util.HashMap;
import java.util.Map;

import org.neo4j.function.ThrowingFunction;
import org.neo4j.internal.kernel.api.exceptions.schema.IndexNotFoundKernelException;
import org.neo4j.internal.schema.IndexDescriptor;
import org.neo4j.kernel.api.index.IndexReader;

/**
 * Cache which maps IndexDescriptors to IndexReaders. This is intended for reusing IndexReaders during a transaction.
 */
public class IndexReaderCache
{
    private final Map indexReaders;
    private final ThrowingFunction indexSupplier;

    public IndexReaderCache( ThrowingFunction indexSupplier )
    {
        this.indexSupplier = indexSupplier;
        this.indexReaders = new HashMap<>();
    }

    public T getOrCreate( IndexDescriptor descriptor ) throws IndexNotFoundKernelException
    {
        var reader = indexReaders.get( descriptor );
        if ( reader == null )
        {
            reader = indexSupplier.apply( descriptor );
            indexReaders.put( descriptor, reader );
        }
        return reader;
    }

    public void close()
    {
        if ( indexReaders.isEmpty() )
        {
            return;
        }

        for ( IndexReader indexReader : indexReaders.values() )
        {
            indexReader.close();
        }
        indexReaders.clear();
    }
}